Systems and methods for controlling grip force of jaws when transitioning between position control mode and force mode

ABSTRACT

Disclosed are systems and methods for achieving a smooth transition in the grip force when the wrist jaws transition between the position and force mode. In the position mode, the desired jaw angle is above a threshold corresponding to an angle at which both jaws are just simultaneously in contact with an object held between the jaws or, if there is no object, when the jaws begin to touch each other. A feedback loop may determine that the jaws are transitioning between the modes based on changes of the desired jaw angle. The feedback loop may analyze the commanded grip force and the measured grip force to determine whether to adjust the commanded grip force during the transition. If so, the feedback loop may adjust the commanded grip force to reduce changes in the measured grip force that is otherwise based on the desired jaw angle.

TECHNICAL FIELD

The subject technology generally relates to robotics and surgicalsystems, and more specifically, to controlling the grip force or openingforce of surgical tools such as wrist jaws of robotically-assistedsurgical systems.

BACKGROUND

Minimally-invasive surgery, MIS, such as laparoscopic surgery, usestechniques that are intended to reduce tissue damage during a surgicalprocedure. Laparoscopic procedures typically call for creating a numberof small incisions in the patient, e.g., in the abdomen, through whichseveral surgical tools such as an endoscope, a scalpel, a grasper, and aneedle, are then inserted into the patient. A gas is injected into theabdomen which insufflates the abdomen thereby providing more spacearound the tips of the tools, making it easier for the surgeon to see(via the endoscope) and manipulate tissue at the surgical site. MIS canalso be performed using a robotic system in which the surgical tools areoperatively attached to the distal ends of robotic arms, and a controlsystem actuates the arm and its attached tool so that the latter mimicsthe movements and tool specific commands of a user input device (UID) asthe latter is being manipulated by a surgeon in their hand.

Surgical tools may include a robotic wrist supporting a pair of opposingjaws. The wrist and the jaws may move in multiple degrees-of-freedom ascontrolled by commands from the remote operator to perform grasping,cutting, suturing, and other surgical tasks. For example, actuators in atool drive of the robotic arm may drive multi-axial motions (e.g. pitchand yaw) of the wrist jaws to pivot, open, close the jaws, or to controlthe grip force or opening force between the jaws while moving the wristto any angular position. The jaws may grasp patient tissue, hold acutting instrument, etc. Precise control of the grip force or openingforce when closing or opening the jaws is critical to prevent damage tothe tissue or to ensure precision cutting by the instrument. Inaddition, the jaws may operate in a positional mode in which the anglebetween the pair of jaws are commanded to a desired jaw angle and aforce mode in which the jaws are commanded to apply a desired gripforce. A smooth transition between the positional mode and the forcemode minimizes undesirable sudden changes in the grip force that maycause an accidental drop of any object being grasped.

SUMMARY

A system and method is disclosed for limiting the grip force generatedby closing robotic wrist jaws while operating in a position control modein which the jaws are commanded to a desired jaw angle prior to beingcommanded to generate a grip force. In the position control mode, orsimply position mode, the desired jaw angle is above a threshold thatcorresponds to an angle at which both jaws are just simultaneously incontact with an object between the jaws or, if there is no object tograsp, when the jaws begin to touch each other. When the desired jawangle is below the threshold, the wrist jaws are operating in a forcecontrol mode, or simply force mode, and the desired jaw angle istranslated into a desired grip force. The disclosed system and methodlimits the maximum amount of grip force when the jaws are closing in theposition mode to prevent damage to tissue that may be grasped by thejaws. The grip force may be estimated or measured. A feedback loop mayanalyze the desired jaw angle and the measured grip force to determineif the jaws are closing in the position mode and if the measured gripforce exceeds a pre-specified maximum grip force threshold. If so, thefeedback loop may calculate a grip force error to limit the measuredgrip force to the pre-specified maximum grip force threshold.

In another aspect, a system and method is disclosed for achieving aminimum jaw opening force by the wrist jaws when operating in theposition mode. Maintaining a minimum jaw opening force while the jawsare opening in the position mode helps the jaws to overcome resistancethat may be preventing the jaws from opening to the desired jaw angle.The opening force representing the jaw opening force and the jaw anglemay be measured or estimated. A feedback loop may analyze the desiredjaw angle, the estimated jaw angle, and the measured jaw opening forceto determine if the jaws are opening in the position mode and if themeasured jaw opening force is below a pre-specified minimum openingforce threshold. If so, the feedback loop may calculate a jaw openingforce error to maintain the jaw opening force above the pre-specifiedminimum opening force threshold.

In another aspect, a system and method is disclosed for achieving asmooth transition in the grip force when the wrist jaws transitionbetween the position mode and the force mode. A smooth transition fromthe position mode to the force mode and vice versa minimizes undesiredsudden changes in the grip force that may cause the wrist jaws toaccidentally drop an object being grasped when the jaws traverse throughthe point of discontinuity between the two modes. In one embodiment, inorder to transition from the position mode to the force mode, adebouncing strategy may be used to ensure that the desired jaw angle issmaller than the threshold between the position and force modes for apre-specified minimum duration before the wrist jaws transition to theforce mode.

In one embodiment, the system and method may determine the desired gripforce from the desired jaw angle and may measure or estimate the gripforce. A feedback loop may analyze the desired jaw angle, the desiredgrip force, and the measured grip force to determine if the jaws aretransitioning from the position mode to the force mode, if an errorbetween the measured grip force and the desired grip force is largerthan a pre-specified maximum force error and if the desired grip forceis increasing. If so, the feedback loop may set the desired grip forceas the current measured grip force minus a pre-specified margin when thejaws transition from the position mode to the force mode.

In one embodiment, the feedback loop may analyze the desired jaw angle,the desired grip force as determined from the desired jaw angle, and themeasured grip force to determine if the jaws are transitioning from theforce mode to the position mode, if the desired grip force is smallerthan a minimum grip force value, if the desired grip force isdecreasing, and if the absolute value of the error between the measuredgrip force and the minimum grip force is smaller than a pre-specifiedmaximum force error. If so, the feedback loop may set the desired gripforce to the minimum grip force value when the jaws transition from theforce mode to the position mode.

A method for controlling grip force generated by jaws of a gripper toolis disclosed. The method may include determining that the jaws aretransitioning between the position mode and the force mode based onchanges of a desired jaw angle between the jaws. During the positionmode the jaws are driven with a commanded jaw angle, which may be thedesired jaw angle. During the force mode, the jaws are driven withcommanded grip force that is determined based on the desired jaw anglehaving a negative value. The method also includes determining based onthe commanded grip force and the measured grip force whether to adjustthe commanded grip force during the transition between the position modeand the force mode. If so, the method further includes adjusting thecommanded grip force to reduce changes in the measured grip force thatis otherwise determined based on the desired jaw angle during thetransition.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are provided together with the followingdescription of various aspects and embodiments of the subject technologyfor a better comprehension of the invention. The drawings and theembodiments are illustrative of the invention, and are not intended tolimit the scope of the invention. It is understood that a person ofordinary skill in the art may modify the drawings to generate drawingsof other embodiments that would still fall within the scope of theinvention.

FIG. 1 is a pictorial view of an example surgical robotic system 1 in anoperating arena, in accordance with aspects of the subject technology.

FIG. 2 is a schematic diagram illustrating one exemplary design of arobotic arm, a tool drive, and a cannula loaded with a robotic surgicaltool, in accordance with aspects of the subject technology.

FIGS. 3A and 3B are schematic diagrams illustrating an exemplary tooldrive with and without a loaded tool, respectively, in accordance withaspects of the subject technology.

FIGS. 4A and 4B are schematic diagrams illustrating the end effector ofan exemplary grasper having a robotic wrist, a pair of opposing jaws,and a pulley and cable system for coupling the robotic wrist and thepair of jaws to the actuators of a tool drive, in accordance withaspects of the subject technology.

FIG. 5 is a block diagram of an exemplary control system for controllingthe position and grip force of an end effector of a robotic surgicaltool, in accordance with aspects of the subject technology.

FIG. 6A is a time plot showing the commanded jaw angle, the measured jawangle, the commanded grip force, and the measured grip force of thewrist jaws when the measured grip force is not limited while the jawsare closing in the position mode.

FIG. 6B is a time plot showing the commanded jaw angle, the measured jawangle, the commanded grip force, and the measured grip force of thewrist jaws when a control system limits the measured grip force to apre-specified maximum threshold during jaw closing in the position mode,in accordance with aspects of the subject technology.

FIG. 7 is a flow chart illustrating a method for feedback control of asurgical robotic system to limit the grip force of the wrist jaws to apre-specified maximum threshold during jaws closing in the position modeby analyzing the desired jaw angle and the measured grip force, inaccordance with aspects of the subject technology.

FIG. 8A is a time plot showing the commanded jaw angle, the measured jawangle, the commanded grip force, and the measured opening force of thewrist jaws when the measured opening force is not maintained above aminimum level while the jaws are opening in the position mode.

FIG. 8B is a time plot showing the commanded jaw angle, the measured jawangle, the commanded grip force, and the measured opening force of thewrist jaws when a control system maintains the measured opening forceabove a pre-specified minimum opening force threshold during jawsopening in the position mode, in accordance with aspects of the subjecttechnology.

FIG. 9 is a flow chart illustrating a method for feedback control of asurgical robotic system to maintain the opening force of the wrist jawsabove a pre-specified minimum opening force threshold during jawsopening in the position mode by analyzing the desired jaw angle, theestimated jaw angle and the measured opening force, in accordance withaspects of the subject technology.

FIG. 10 is a block diagram of an exemplary control system forcontrolling the position and grip force of an end effector of a roboticsurgical tool when the end effector is in the position mode or forcemode, or when the end effector transitions between the position mode andthe force mode, in accordance with aspects of the subject technology.

FIG. 11A is a time plot showing the commanded jaw angle, the measuredjaw angle, the commanded grip force, the measured grip force of thewrist jaws, and activities of a grip force controller when the jaw angleis set to be around the threshold between the position mode and theforce mode without a debouncing algorithm.

FIG. 11B is a time plot showing the commanded jaw angle, the measuredjaw angle, the commanded grip force, the measured grip force of thewrist jaws, and activities of a grip force controller when a controlsystem employs a debouncing algorithm when setting the jaw angle to bearound the threshold between the position mode and the force mode, inaccordance with aspects of the subject technology.

FIG. 12A is a time plot showing the commanded jaw angle, the measuredjaw angle, the commanded grip force, and the measured grip force of thewrist jaws when changes in the measured grip force is not constrainedwhen the jaws transition from the position mode to the force mode andback to the position mode.

FIG. 12B is a time plot showing the commanded jaw angle, the measuredjaw angle, the commanded grip force, and the measured grip force of thewrist jaws when a control system constrains changes in the grip force asthe jaws transition between the position mode and the force mode, inaccordance with aspects of the subject technology.

FIG. 13 is a flow chart illustrating a method for a feedback control ofa surgical robotic system to employ a debouncing algorithm when settingthe desired jaw angle of the wrist jaws around the threshold between theposition mode and the force mode, or to adjust the commanded grip forceto limit changes in the measured grip force when the jaws transitionbetween the position mode and the force mode, in accordance with aspectsof the subject technology.

FIG. 14 is a block diagram illustrating exemplary hardware components ofa surgical robotic system, in accordance with aspects of the subjecttechnology.

DETAILED DESCRIPTION

Examples of various aspects and variations of the subject technology aredescribed herein and illustrated in the accompanying drawings. Thefollowing description is not intended to limit the invention to theseembodiments, but rather to enable a person skilled in the art to makeand use this invention.

Disclosed are feedback control systems and methods for controlling thegrip force or opening force of end effectors of surgical robotic armssuch as wrist jaws. Wrist jaws may be coupled to actuators of a tooldrive through cables for effecting multi-axial motions of the wristjaws. The feedback control system may command the wrist jaw to a pitchangle, a yaw angle, and a jaw angle between the jaws. When the commandedjaw angle is above a threshold, also referred to as a threshold fordetent, the wrist jaws may operate in the position mode for moving thewrist jaws to a commanded position and orientation. The commanded jawangle may also be referred to as the desired jaw angle. When thecommanded jaw angle is below the threshold for detent, the wrist jawsmay operate in the force mode from the position and orientation of theposition mode and a desired grip force is generated by a grip forcecontroller based on the commanded jaw angle. In one embodiment, thefeedback control system may limit the maximum grip force when the jawsare closing in the position mode by analyzing the desired jaw angle andmeasuring or estimating the grip force as actually applied to determineif the measured grip force exceeds a pre-specified maximum grip forcethreshold. If so, the feedback control system may calculate a grip forceerror to adjust the grip force so that the measured grip force islimited to the pre-specified maximum grip force threshold.

In one embodiment, the feedback control system may maintain the minimumjaw opening force when the jaws are opening in the position mode. Thefeedback control system may measure or estimate the jaw angle asactually applied. The feedback control system may also measure orestimate the grip force or opening force of the jaws as actuallyapplied. By analyzing the desired jaw angle, the measured jaw angle andthe measured jaw opening force, the feedback control system maydetermine if the jaws are in the position mode, the difference betweenthe desired jaw angle and the estimated jaw angle is larger than athreshold, and if the measured jaw opening force is smaller than apre-specified minimum opening force threshold. If so, feedback controlsystem may calculate an opening force error to adjust the grip force oropening force to maintain the measured jaw opening force above thepre-specified minimum opening force threshold.

In one embodiment, the feedback control system may use a debouncingalgorithm to prevent the wrist jaws from oscillating between theposition mode and the force mode when the jaw angle is set arounddetent. The feedback control system may determine if the desired jawangle is smaller than the threshold for detent for a pre-specifiedduration. If so, the feedback control system may switch the wrist jawsfrom the position mode to the force mode. In one embodiment, thedebouncing algorithm may be one-sided so that the wrist jaws maytransition back to the position mode as soon as the desired jaw angle islarger than or equal to the threshold.

In one embodiment, the feedback control system may minimize undesiredsudden changes in the grip force when transitioning between the positionmode and the force mode. The grip force controller may calculate thecurrent command for a desired grip force from the desired jaw angle. Thefeedback control system may measure or estimate the grip force asactually applied. The feedback control system may analyze the desiredjaw angle, the desired grip force, and the measured grip force todetermine if the jaws are transitioning from the position mode to theforce mode and if an error between the measured grip force and thedesired grip force is larger than a pre-specified maximum force errorand if the desired grip force is increasing. If so, the feedback controlsystem may set the grip force as the measured grip force minus apre-specified margin when transitioning from the position mode to theforce mode.

In one embodiment, the feedback control system may analyze the desiredjaw angle, the desired grip force, and the measured grip force todetermine if the jaws are transitioning from the force mode to theposition mode, if the desired grip force is smaller than a pre-specifiedminimum grip force value, if the desired grip force is decreasing and ifthe absolute value of the error between the measured grip force and theminimum grip force is smaller than a pre-specified maximum force error.If so, the feedback control system may set the grip force to thepre-specified minimum grip force value when transitioning from the forcemode to the position mode. In one embodiment, the pre-specified minimumgrip force value may be set to 3N.

FIG. 1 is a pictorial view of an example surgical robotic system 1 in anoperating arena, in accordance with aspects of the subject technology.The robotic system 1 includes a user console 2, a control tower 3, andone or more surgical robotic arms 4 at a surgical robotic platform 5,e.g., a table, a bed, etc. The arms 4 may be mounted to a table or bedon which the patient rests as shown in the example of FIG. 1 , or theymay be mounted to a cart separate from the table or bed. The system 1can incorporate any number of devices, tools, or accessories used toperform surgery on a patient 6. For example, the system 1 may includeone or more surgical tools 7 used to perform surgery. A surgical tool 7may be an end effector that is attached to a distal end of a surgicalarm 4, for executing a surgical procedure.

Each surgical tool 7 may be manipulated manually, robotically, or both,during the surgery. For example, the surgical tool 7 may be a tool usedto enter, view, or manipulate an internal anatomy of the patient 6. Inone aspect, the surgical tool 7 is a grasper such as wrist jaws that cangrasp tissue of the patient. The surgical tool 7 may be configured to becontrolled manually by a bedside operator 8, robotically via actuatedmovement of the surgical robotic arm 4 to which it is attached, or both.The robotic arms 4 are shown as being table-mounted but in otherconfigurations the arms 4 may be mounted to a cart, the ceiling or asidewall, or to another suitable structural support.

A remote operator 9, such as a surgeon or other human operator, may usethe user console 2 to remotely manipulate the arms 4 and their attachedsurgical tools 7, e.g., referred to here as teleoperation. The userconsole 2 may be located in the same operating room as the rest of thesystem 1 as shown in FIG. 1 . In other environments however, the userconsole 2 may be located in an adjacent or nearby room, or it may be ata remote location, e.g., in a different building, city, or country. Theuser console 2 may comprise a seat 10, foot-operated controls 13, one ormore handheld user input devices, UID 14, and at least one user display15 that is configured to display, for example, a view of the surgicalsite inside the patient 6. In the example user console 2, the remoteoperator 9 is sitting in the seat 10 and viewing the user display 15while manipulating a foot-operated control 13 and a handheld UID 14 inorder to remotely control the arms 4 and the surgical tools 7 that aremounted on the distal ends of the arms 4.

In some variations, the bedside operator 8 may operate the system 1 inan “over the bed” mode in which the beside operator 8 (user) is at aside of the patient 6 and is simultaneously manipulating arobotically-driven tool (an end effector that is attached to the arm 4)with a handheld UID 14 held in one hand, and a manual laparoscopic toolin another hand. For example, the bedside operator's left hand may bemanipulating the handheld UID to control a robotically-driven tool,while the bedside operator's right hand may be manipulating a manuallaparoscopic tool. In this particular variation of the system 1, thebedside operator 8 can perform both robotic-assisted minimally invasivesurgery and manual laparoscopic surgery on the patient 6.

During an example procedure (surgery), the patient 6 is prepped anddraped in a sterile fashion to achieve anesthesia. Initial access to thesurgical site may be performed manually while the arms of the roboticsystem 1 are in a stowed configuration or withdrawn configuration (tofacilitate access to the surgical site.) Once access is completed,initial positioning or preparation of the robotic system 1 including itsarms 4 may be performed. Next, the surgery proceeds with the remoteoperator 9 at the user console 2 utilizing the foot-operated controls 13and the UIDs 14 to manipulate the various end effectors and perhaps animaging system, to perform the surgery. Manual assistance may also beprovided at the procedure bed or table, by sterile-gowned bedsidepersonnel, e.g., the bedside operator 8 who may perform tasks such asretracting tissues, performing manual repositioning, and tool exchangeupon one or more of the robotic arms 4. Non-sterile personnel may alsobe present to assist the remote operator 9 at the user console 2. Whenthe procedure or surgery is completed, the system 1 and the user console2 may be configured or set in a state to facilitate post-operativeprocedures such as cleaning or sterilization and healthcare record entryor printout via the user console 2.

In one embodiment, the remote operator 9 holds and moves the UID 14 toprovide an input command to move a robot arm actuator 17 in the roboticsystem 1. The UID 14 may be communicatively coupled to the rest of therobotic system 1, e.g., via a console computer system 16. The UID 14 cangenerate spatial state signals corresponding to movement of the UID 14,e.g. position and orientation of the handheld housing of the UID, andthe spatial state signals may be input signals to control a motion ofthe robot arm actuator 17. The robotic system 1 may use control signalsderived from the spatial state signals, to control proportional motionof the actuator 17. In one embodiment, a console processor of theconsole computer system 16 receives the spatial state signals andgenerates the corresponding control signals. Based on these controlsignals, which control how the actuator 17 is energized to move asegment or link of the arm 4, the movement of a corresponding surgicaltool that is attached to the arm may mimic the movement of the UID 14.Similarly, interaction between the remote operator 9 and the UID 14 cangenerate for example a grip control signal that causes a jaw of agrasper of the surgical tool 7 to close and grip the tissue of patient6.

The surgical robotic system 1 may include several UIDs 14, whererespective control signals are generated for each UID that control theactuators and the surgical tool (end effector) of a respective arm 4.For example, the remote operator 9 may move a first UID 14 to controlthe motion of an actuator 17 that is in a left robotic arm, where theactuator responds by moving linkages, gears, etc., in that arm 4.Similarly, movement of a second UID 14 by the remote operator 9 controlsthe motion of another actuator 17, which in turn moves other linkages,gears, etc., of the robotic system 1. The robotic system 1 may include aright arm 4 that is secured to the bed or table to the right side of thepatient, and a left arm 4 that is at the left side of the patient. Anactuator 17 may include one or more motors that are controlled so thatthey drive the rotation of a joint of the arm 4, to for example change,relative to the patient, an orientation of an endoscope or a grasper ofthe surgical tool 7 that is attached to that arm. Motion of severalactuators 17 in the same arm 4 can be controlled by the spatial statesignals generated from a particular UID 14. The UIDs 14 can also controlmotion of respective surgical tool graspers. For example, each UID 14can generate a respective grip signal to control motion of an actuator,e.g., a linear actuator, which opens or closes jaws of the grasper at adistal end of surgical tool 7 to grip tissue within patient 6.

In some aspects, the communication between the platform 5 and the userconsole 2 may be through a control tower 3, which may translate usercommands that are received from the user console 2 (and moreparticularly from the console computer system 16) into robotic controlcommands that are transmitted to the arms 4 on the robotic platform 5.The control tower 3 may also transmit status and feedback from theplatform 5 back to the user console 2. The communication connectionsbetween the robotic platform 5, the user console 2, and the controltower 3 may be via wired and/or wireless links, using any suitable onesof a variety of data communication protocols. Any wired connections maybe optionally built into the floor and/or walls or ceiling of theoperating room. The robotic system 1 may provide video output to one ormore displays, including displays within the operating room as well asremote displays that are accessible via the Internet or other networks.The video output (video feed) may also be encrypted to ensure privacyand all or portions of the video output may be saved to a server orelectronic healthcare record system.

FIG. 2 is a schematic diagram illustrating one exemplary design of arobotic arm, a tool drive, and a cannula loaded with a robotic surgicaltool, in accordance with aspects of the subject technology. As shown inFIG. 2 , the example surgical robotic arm 112 may include a plurality oflinks (e.g., a link 202) and a plurality of actuated joint modules(e.g., a joint 204) for actuating the plurality of links relative to oneanother. The joint modules may include various types, such as a pitchjoint or a roll joint, which may substantially constrain the movement ofthe adjacent links around certain axes relative to others. Also shown inthe exemplary design of FIG. 2 is a tool drive 210 attached to thedistal end of the robotic arm 112. The tool drive 210 may include acannula 214 coupled to its end to receive and guide a surgicalinstrument 220 (e.g., endoscopes, staplers, etc.). The surgicalinstrument (or “tool”) 220 may include an end effector 222 at the distalend of the tool. The plurality of the joint modules of the robotic arm112 can be actuated to position and orient the tool drive 210, whichactuates the end effector 222 for robotic surgeries.

FIGS. 3A and 3B are schematic diagrams illustrating an exemplary tooldrive with and without a loaded tool, respectively, in accordance withaspects of the subject technology. As shown in FIGS. 3A and 3B, in onevariation, the tool drive 210 may include an elongated base (or “stage”)310 having longitudinal tracks 312 and a tool carriage 320, which isslidingly engaged with the longitudinal tracks 312. The stage 310 may beconfigured to couple to the distal end of a robotic arm such thatarticulation of the robotic arm may position and/or orient the tooldrive 210 in space. Additionally, the tool carriage 320 may beconfigured to receive a tool base 352 of the tool 220, which may alsoinclude a tool shaft 354 extending from the tool base 352 and throughthe cannula 214, with the end effector 222 (not shown) disposed at thedistal end.

Additionally, the tool carriage 320 may actuate a set of articulatedmovements of the end effector, such as through a cable system or wiresmanipulated and controlled by actuated drives (the terms “cable” and“wire” are used interchangeably throughout this application). The toolcarriage 320 may include different configurations of actuated drives.For example, the rotary axis drives may include a motor with a hollowrotor and a planetary gear transmission at least partially disposedwithin the hollow rotor. The plurality of rotary axis drives may bearranged in any suitable manner. For example, the tool carriage 320 mayinclude six rotary drives 322A-322F arranged in two rows, extendinglongitudinally along the base that are slightly staggered to reducewidth of the carriage and increase the compact nature of the tool drive.As clearly shown in FIG. 3B, rotary drives 322A, 322B, and 322C may begenerally arranged in a first row, while rotary drives 322D, 322E, and322F may be generally arranged in a second row that is slightlylongitudinally offset from the first row.

FIGS. 4A and 4B are schematic diagrams illustrating the end effector ofan exemplary grasper having a robotic wrist, a pair of opposing jaws,and a pulley and cable system for coupling the robotic wrist and thepair of jaws to the actuators of a tool drive, in accordance withaspects of the subject technology. Note that although the following toolmodel and controller design are described with reference to theexemplary surgical robotic grasper, the proposed control system forposition and grip force control may be adapted to any tools that includean end effector coupled to a tool shaft via a robotic wrist, whichallows multi-axial motion (e.g., pitch and yaw) of the end effector.Similar tools include, but not limited to, graspers, grippers, forceps,needle drivers, retractors, and cautery instruments.

As shown in FIG. 4A, the pair of opposing jaws 401A and 401B are movablycoupled to a first yoke 402 of the robotic wrist via an extended axle412 along a first axis 410. The first yoke 402 may be movably coupled toa second yoke 403 of the robotic wrist via a second extended axle 422along a second axis 420. The pair of jaws 401A and 401B may each becoupled or integrally formed with pulleys 415A and 415B respectively,via the extended axle 412, so that both jaws can rotate about the axis410. Pulleys 425A, 425B, 425C and 425D are coupled to the extended axle422 and rotate around the axis 420. The pulleys 425A, 425B, 425C and425D are arranged into a first set of pulleys 425B and 425C on one sideof the yoke 402 and a second set of pulleys 425A and 425D on the otherside of the yoke 402. The pulleys 425A and 425C are outer pulleys andthe pulleys 425B and 425D are inner pulleys. Similarly, the third set ofpulleys 435A, 435B, 435C and 435D are coupled to a third extended axle432 and rotate around the axis 430, which is parallel to the axis 420.

The grasper 220 can be actuated to move one or both of the jaws 401A and401B in a variety of ways around the axis 410. For example, the jaws401A and 401B may open and close relative to each other. The jaws 401Aand 401B may also be actuated to rotate together as a pair to provide ayaw motion of the grasper 220. In addition, the first yoke 402, thepulleys 415A and 415B, and the jaws 401A and 401B can rotate about theaxis 420 to provide a pitch motion of the grasper 220. The motion of therobotic wrist and/or the jaws of the tool can be actuated by controllingfour independent cables 405A-405D. As shown in FIG. 4A, cable 405A maystart (or terminates) from one side of the pulley 415A and route alongpulleys 425A and 435A, and cable 405B is configured to terminate at theother side of the pulleys 415A and route through pulleys 425B and 435B.Similarly, another pair of cables 405C and 405D can be coupled to thejaw 401B. For example, cable 405C extends from one side of the pulley415B to pulleys 425C and 435C; and cable 405D routes through pulleys425D and 435D and terminates at the other side of pulley 415B. The thirdset of pulleys 435A, 435B, 435C and 435D are arranged in such away as tokeep the cables 405A-405D affixing to the second set of pulleys425A-425D and prevent the cables from slipping or sliding relative tothe pulleys 425A-425D.

As shown in FIGS. 4A and 4B, the grasper 220 can be actuated to move thejaws 401A and 401B in a variety of ways such as grasping (e.g., jawsrotating independently about axis 410), yaw (e.g., jaws rotatingtogether about axis 410), and pitch (e.g., jaws rotating about axis 420)by imparting motion to one or more of the pulleys 415A, 415B, 425A,425B, 425C, and 425D to thereby impart motion on the first yoke 402and/or one or both of the jaws 401A and 401B. Cables 405A-405D can begrouped into two antagonistic pairs, that is, when one cable of theantagonistic pair is actuated or tensioned, while the other cable isloosened, the jaw will rotate in one direction. Whereas when only theother cable is tensioned, the jaw will rotate in an opposite direction.

For example, cables 405A and 405B are the first antagonistic pair formoving jaw 401A, and cables 405C and 405D are the second antagonisticpair for controlling jaw 401B. When cable 405A is tensioned (e.g., by atleast one of the rotary drives 322 a-322 f) while cable 405B isloosened, jaw 401A closes (moving towards the opposite jaw 401B). On theother hand, when cable 405B is tensioned and cable 405A is loosened, jaw401A opens (moving away from the opposite jaw 401B). Similarly, whentensioned, cable 405C closes jaw 401B (moving towards the opposite jaw401A) and cable 405D opens jaw 401B (moving away from the opposite jaw401A) while the other cable loosens. As another example, grip forcebetween the jaw 401A and jaw 401B can be achieved by continuing totension both cable 405A and cable 405C (while cable 405B and cable 405Dare loosened) after the jaws are closed (touching each other).

In case when both cables of an antagonistic pair are tensioned at thesame time while both cables of the other pair are loosened, the pulley415A or pulley 415B do not rotate. Instead, the first yoke 402 togetherwith the jaws 401A and 401B are imparted by the pulleys 415A and 415B topitch about the axis 420. For example, when the pair of cables 405A and405B are both tensioned simultaneously while the pair of cable 405C and405D are loosened, the jaws (together with the yoke 402) pitch out ofthe plane of the paper. Whereas when both cables 405C and 405D aretensioned simultaneously and the pair 405A and 405B are kept loose, thejaws pitch into the plane of the paper.

FIG. 4B is a schematic diagram illustrating example angle definitionsfor various motions of the grasper 220, in accordance with aspects ofthe subject technology. The angles are defined in reference to axes 410and 420, as well as an axis 452 of the first yoke 402 and an axis 453 ofthe second yoke 403. For example, as shown in FIG. 4B, an angle (θ₁)between axis 452 and the axis 453 may represent the rotation angle ofthe yoke 402 around axis 420, which may also be defined as the pitchangle (θ_(pitch)) of the grasper 220 (while in FIG. 4A, the axis 452 ofthe yoke 402 is superimposed over the axis 453 of the yoke 403 becausethe jaws are staying in the reference position, i.e., no pitch motions).In addition, angles (θ₂) and (θ₃) can represent the angles between eachof the jaws 401A and 401B and the axis 452 of the yoke 402 (as theorigin), respectively. To differentiate the sides of the axis 452,angles (θ₂) and (θ₃) may take on different signs. For example, angle(θ₂) is negative and angle (θ₃) is positive, as illustrated in FIG. 4B.

In order to perform control tasks, it is often beneficial to define aconsistent coordinate frame for the joint angles. For example, we mayfurther define the jaw angle (θ_(jaw)) as the angle between the two jaws401A and 401B, and the yaw angle (θ_(yaw)) as the angle between the axis452 and the line bisecting the jaw angle. As mentioned, pitch angle(θ_(pitch)) may be defined as angle (θ₁) between axis 452 and the axis453. Therefore:

$\begin{matrix}\{ \begin{matrix}{\theta_{yaw} = {\frac{1}{2}( {\theta_{2} + \theta_{3}} )}} \\{\theta_{jaw} = ( {\theta_{3} - \theta_{2}} )} \\{\theta_{pitch} = \theta_{1}}\end{matrix}  & {{Equation}\mspace{14mu} 1}\end{matrix}$

Described below is a method and system for controlling angular positionand grip force of a distal end effector of a robotic surgicalinstrument. The end effector may include a robotic wrist and a pair ofopposing members (e.g., jaws or claws), each being movable between anopen position and a closed position actuated by two antagonistic wires.A total of four wires may each be driven by an independent actuator ormotor, as illustrated in FIGS. 3 and 4 . The control system may includefeedback loops involving position and velocity feedback from theactuators and force feedback measured on the four wires, to effectdesired position and grip force. In some implementations, the actuatorcontrollers may be running a position plus feedforward current mode. Forexample, a position controller in the position mode may drive the distalend effector to the desired angular position in space based on thepositional feedback, while in the force mode a grip force controllerprovides additional feedforward current based on the grip force measuredby load cells on the four wires to achieve the desired grip forcebetween the opposing members.

FIG. 5 is a block diagram illustrating a high-level control system forcontrolling a surgical tool, in accordance with aspects of the subjecttechnology. The control system comprises an input 560, a controller 562,a plant 564, an output 568, and sensors and estimators 566 on a feedbackpath between the output 568 and the controller 562. The plant 564 mayinclude tool actuators and end effector (e.g., rotary drives 322A-322Fof FIG. 3B and cables 405A-405D of wrist jaws of FIG. 4A; see alsoactuator units 510 and cable and wrist links 512 in FIG. 10 ). Thecontroller 562 may include one or more processors configured by softwareinstructions stored on a memory to calculate motions of the plant 564 inresponse to the input 560, which may indicate a desired movement of thesurgical tool's end effector, such as the desired θ_(pitch), desiredθ_(yaw), and desired θ_(jaw) of the wrist jaws of FIG. 4B. Commands thusgenerated by the controller 562 may drive the tool actuators tofacilitate the desired movement of the end effector. In one embodiment,the desired θ_(pitch), θ_(yaw), and θ_(jaw) may be generated by the UID14 under the control of the remote operator 9 of FIG. 1 . The output568, such as position, velocity, cable tension, and grip force oropening force of the end effector, may be directly measured or estimatedby the sensors and estimators 566 and fed back to the controller 562 forclosed-loop control.

In one embodiment, when the desired jaw angle θ_(jaw) of the wrist jawsis greater than or equal to a threshold, the desired θ_(jaw), which isalso referred to as the commanded θ_(jaw), may be treated as a positioncontrol command in the position mode. The threshold is used to determinedetent, and may correspond to an angle at which both jaws are justsimultaneously in contact with the object(s) in between. In case thereare no objects to grasp, the threshold is zero degree when the jawsbegin to touch each other. In the position mode, the controller 562 maytranslate the desired θ_(jaw), as well as the desired θ_(pitch) anddesired θ_(yaw), into corresponding actuator position commands to drivethe wrist jaws to the desired position and orientation. When the desiredθ_(jaw) is below the threshold, the wrist jaws are operating in a forcecontrol mode, or simply force mode, and the desired jaw angle istranslated into a desired grip force command. The controller 562 maygenerate a current command in addition to the position command toachieve the desired grip force.

In one embodiment, the controller 562 may limit the maximum amount ofgrip force when the jaws are closing in the position mode to preventdamage to tissue that may be grasped by the jaws. The grip force of thejaws may be estimated or measured by the sensors and estimators 566. Thecontroller 562 may analyze the desired θ_(jaw) and the measured gripforce to determine if the jaws are closing in the position mode and ifthe measured grip force exceeds a pre-specified maximum grip forcethreshold. If so, the controller 562 may calculate a grip force error tolimit the measured grip force to the pre-specified maximum grip forcethreshold. For example, to determine if the jaws are closing in theposition mode, the controller 562 may first verify that the desiredθ_(jaw) is greater than or equal to the threshold for detent, and thusin the position mode, for more than a pre-specified duration. Thecontroller 562 may employ a debouncing technique to verify that thedesired θ_(jaw) has been decreasing for a pre-specified length of time.In one embodiment if the desired θ_(jaw) are sampled at a periodicfrequency, the controller 562 may verify that the samples of the desiredθ_(jaw) have been decreasing for a pre-specified number of samples.

To determine if the measured grip force exceeds a pre-specified maximumgrip force threshold, the controller 562 may also employ a debouncingtechnique. In one embodiment, the feedback control loop of the controlsystem of FIG. 5 may operate with a loop cycle time. A grip forcecounter may increase by one count for every control loop cycle duringwhich the measured grip force is less than the maximum grip forcethreshold minus a margin. In one embodiment, the grip force counter maystop incrementing after it reaches a maximum count. When the measuredgrip force is larger than the maximum grip force threshold, the gripforce counter may reset. The debouncing technique may declare that themeasured grip force exceeds the maximum grip force threshold for anentirety of a window that spans a number of loop cycles equaling to thegrip force counter when the measured grip force is larger than themaximum grip force minus the margin anywhere within the window.

As an example, assume the measured grip force is initially below themaximum grip force threshold minus the margin and the grip force counteris incrementing. When the measured grip force increases beyond themaximum grip force threshold, the grip force counter may be reset. Thefeedback control loop of the controller 562 may attempt to change theactuator position commands to drive the wrist jaws to limit the measuredgrip force to the maximum grip force threshold. However, even if themeasured grip force drops below the maximum grip force threshold butstays above the maximum grip force threshold minus the margin, thefeedback control loop may still consider the measured grip force to belarger than the maximum grip force threshold so as to limit the maximummeasured grip force. Assume the measured grip force dips below themaximum grip force threshold minus the margin for only a few loop cyclesbut then increases above this level again. The grip force counter mayincrement to the number of loop cycles that the measured grip force wasbriefly below the maximum grip force threshold minus the margin. As longas the measured grip force stays above the maximum grip force thresholdminus the margin within a window that spans a number of loop cyclesequaling to the grip force counter (e.g., the number of loop cycles thatthe measured grip force dipped briefly below the maximum grip forcethreshold minus the margin), the feedback control loop may stillconsider the measured grip force to be larger than the maximum gripforce threshold for the entire duration of the window so as to limit themaximum measured grip force.

When the controller 562 determines that the jaws are closing in theposition mode and that the measured grip force exceeds the maximum gripforce threshold, the controller may limit the measured grip force to themaximum grip force threshold. In one embodiment, the controller 562 maycalculate a grip force error that is the difference between the maximumgrip force threshold and the measured grip force. A zero steady-statetype controller, such as a proportional plus integral (PI) forcecontroller, may be deployed to receive the grip force error to maintainor limit the measured grip force at the maximum grip force threshold.The output of the PI force controller may be combined with the output ofthe inverse kinematic matrix that operates on errors in the desiredposition and orientation of the wrist jaws to generate compensatedactuator position commands. The compensated actuator position commandsare added to the existing actuator position commands to drive the wristjaws to limit the maximum amount of grip force when the jaws are closingin the position mode at the desired position and orientation.

FIG. 6A is a time plot showing the commanded θ_(jaw) 603, the measuredθ_(jaw) 605, the commanded grip force 607, and the measured grip force609 of the wrist jaws when the measured grip force 609 is not limitedwhile the jaws are closing in the position mode. The threshold θ_(jaw)between the position mode and the force mode is set at zero so that whenthe commanded θ_(jaw) 603 is greater than or equal to zero degree, thewrist jaws are operating in the position mode. When the commandedθ_(jaw) 603 is less than zero degree, the wrist jaws are operating inthe force mode.

FIG. 6A shows that from 20 to 35 second and again from 44 to 47 second,the wrist jaws are operating in the position mode. The measured θ_(jaw)605 stays within a relatively narrow range even as the commanded θ_(jaw)603 changes within the position mode or within the force mode,presumably because the jaws are grasping an object. During the positionmode, the commanded grip force 607, which is the desired grip force, maybe set to a default value of zero N because the wrist jaws are notoperating in the force mode. However, the measured grip force 609 may bemuch larger. For example, from 26 to 28 second and from 31 to 35 second,when the jaws are closing in the position mode or are held in the closedposition, the measured grip force 609 exceeds 10 N and may go as high as15 N because the measured grip force is not limited. In the force mode(e.g., 35-44 second and after 47 sec), the grip force controller may setthe commanded grip force 607 as a function of the commanded θ_(jaw) 603and the feedback control loop may keep the measured grip force 609 to bethe same as the commanded grip force 607.

FIG. 6B is a time plot showing the commanded θ_(jaw) 613, the measuredθ_(jaw) 615, the commanded grip force 617, and the measured grip force619 of the wrist jaws when a control system limits the measured gripforce to a pre-specified maximum grip force threshold during jaw closingin the position mode, in accordance with aspects of the subjecttechnology. The maximum grip force threshold is set to 8.5 N.

In FIG. 6B, the time plot of the commanded θ_(jaw) 613 and the measuredθ_(jaw) 615 is the same as the command θ_(jaw) 603 and the measuredθ_(jaw) 605 of FIG. 6A when the measured grip force is not limited.During the position mode, the commanded grip force 617 is again set bythe grip force controller to the default value of zero N. However, themeasured grip force 619 is limited by the grip force controller to themaximum grip force threshold of 8.5 N during the position mode when thejaws are closing or are held in the closed position (e.g., 27-30 second,32-36 sec, and 41-45 sec). Note that the limit on the maximum grip forcein the position mode has no effect on the force mode. Thus, in the forcemode, the measured grip force 619 may be allowed to exceed the maximumgrip force threshold of 8.5 N by following the commanded grip force 617.

FIG. 7 is a flow chart illustrating a method 700 for feedback control ofa surgical robotic system to limit the grip force of the wrist jaws to apre-specified maximum threshold during jaws closing in the position modeby analyzing the desired jaw angle and the measured grip force, inaccordance with aspects of the subject technology. The method 700 may beimplemented by the controller 562 of the control system of FIG. 5 thatreceives the desired θ_(jaw) from user input and the measured grip forcefrom sensors and estimators 566 to generate actuator position commandsfor driving the wrist jaws.

In block 701, the method 700 determines if the wrist jaws are in theposition mode. In one embodiment, block 701 may determine if the desiredθ_(jaw) is greater than or equal to the threshold θ_(jaw) between theposition mode and the force mode for more than a pre-specified timeperiod to confirm that the wrist jaws are in the position mode. In oneembodiment, the threshold θ_(jaw) may be set to zero. If the wrist jawsare not in the position mode, the wrist jaws are in the force mode andthe grip force is not limited. In block 709, the method 700 generatesactuator position commands without placing a constraint on the gripforce. In one embodiment, block 709 translates the desired θ_(jaw) intoa desired grip force command to achieve the desired grip force inaddition to generating the actuator position commands.

If the jaws are in the position mode, block 703 determines if the jawsare closing. In one embodiment, block 703 may employ a debouncingtechnique to determine if the desired θ_(jaw) has been decreasing for apre-specified duration or for a pre-specified number of samples. In oneembodiment, the jaws may be considered closing if the desired θ_(jaw) isheld at a quiescent state without increasing. If the jaws are notclosing, the grip force is not limited even in the position mode. Themethod 700 defaults to block 709 to generate actuator position commandswithout placing a constraint on the grip force.

If the jaws are closing in the position mode, block 705 determines ifthe measured grip force exceeds a pre-specified maximum grip forcethreshold. In one embodiment, block 705 may employ a debouncingtechnique to determine if the measured grip force is larger than themaximum grip force threshold minus a margin anywhere within a windowthat spans a number of samples equaling to a grip force counter. In oneembodiment, the measured grip force may be sampled at a loop cycle timeof the feedback control system of FIG. 5 . The grip force counter mayincrement by one for every control loop cycle during which the measuredgrip force is less than the maximum grip force threshold minus themargin. When the measured grip force is larger than the maximum gripforce threshold, the grip force counter may reset. As long as themeasured grip force exceeds the maximum grip force threshold minus themargin anywhere within the window that spans the number of samplesequaling to the grip force counter, the measured grip force isconsidered to exceed the maximum grip force threshold for the entirewindow. Otherwise, the measured grip force does not exceed the maximumgrip force threshold and the method 700 defaults to block 709 togenerate actuator position commands without placing a constraint on thegrip force.

If the measured grip force exceeds the maximum grip force thresholdwhile the jaws are closing in the position mode, block 707 generatescompensated actuator position commands to limit the measured grip forceto the maximum grip force threshold. In one embodiment, block 707 maycalculate a grip force error that is the difference between the maximumgrip force threshold and the measured grip force. A zero steady-statetype controller, such as a proportional plus integral (PI) forcecontroller, may receive the grip force error to generate a compensatedgrip force command. The output of the PI force controller may becombined with the output of the inverse kinematic matrix that operateson errors in the desired position and orientation of the wrist jaws togenerate the compensated actuator position commands. The compensatedactuator position commands may be added to existing actuator positioncommands to drive the wrist jaws so as to limit the measured grip forceto the maximum grip force threshold.

In another aspect, the controller 562 may maintain a minimum jaw openingforce by the wrist jaws when operating in the position mode. The minimumjaw opening force may also be referred to as the minimum grip force.Maintaining a minimum jaw opening force while the jaws are opening inthe position mode helps the jaws to overcome resistance that may bepreventing the jaws from opening to the desired jaw angle. The jaw angleand the opening force of the jaws may be estimated or measured by thesensors and estimators 566. The controller 562 may analyze the desiredθ_(jaw), the estimated θ_(jaw), and the measured opening force todetermine if the jaws are opening in the position mode, if the jaw angleerror between the desired θ_(jaw) and the estimated θ_(jaw) is largerthan a threshold, and if the measured opening force is below apre-specified minimum jaw opening force threshold. If so, the controller562 may calculate an opening force error between the pre-specifiedminimum jaw opening force threshold and the measured opening force tomaintain the measured opening force above the pre-specified minimum jawopening force threshold.

In one embodiment, to determine if the jaws are opening in the positionmode, the controller 562 may first verify that the desired θ_(jaw) isgreater than or equal to the threshold for detent, and thus in theposition mode, for more than a pre-specified duration. The controller562 may then determine if the opening jaws in the position mode aremeeting resistance that prevents the jaws from opening to the desiredθ_(jaw). In one embodiment, the controller 562 may employ a debouncingtechnique to verify that the desired θ_(jaw) is larger than theestimated θ_(jaw) and that the θ_(jaw) error, which is the differencebetween the desired θ_(jaw) and the estimated θ_(jaw), is larger than anθ_(jaw) error threshold for a pre-specified length of time. In oneembodiment if the desired θ_(jaw) and the estimated θ_(jaw) are sampledat a periodic frequency, the controller 562 may verify that the θ_(jaw)error is larger than the θ_(jaw) error threshold for a pre-specifiednumber of samples.

To determine if the measured opening force is below the pre-specifiedminimum jaw opening force threshold, the controller 562 may also employa debouncing technique. A jaw opening force counter may increase by onecount for every control loop cycle during which the measured openingforce is larger than the minimum jaw opening force threshold plus amargin. In one embodiment, the jaw opening force counter may stopincrementing after it reaches a maximum count. When the measured openingforce is less than the minimum jaw opening force threshold, the jawopening force counter may reset. The debouncing technique may declarethat the measured opening force is below the minimum jaw opening forcethreshold for an entirety of a window that spans a number of loop cyclesequaling to the jaw opening force counter when the measured openingforce is less than the minimum jaw opening force threshold plus themargin anywhere within the window.

As an example, assume the measured opening force is initially above theminimum jaw opening force threshold plus the margin and the jaw openingforce counter is incrementing. When the measured opening force dropsbelow the minimum jaw opening force threshold, the jaw opening forcecounter may be reset. The feedback control loop of the controller 562may attempt to change the actuator position commands to drive the wristjaws to maintain the measured opening force above the minimum jawopening force threshold. However, even if the measured opening forceincreases above the minimum jaw opening force threshold but stays belowthe minimum jaw opening force threshold plus the margin, the feedbackcontrol loop may still consider the measured opening force to be smallerthan the minimum jaw opening force threshold so as to maintain theminimum jaw opening force. Assume the measured opening force rises abovethe minimum jaw opening force threshold plus the margin for only a fewloop cycles but then dips below this level again. The jaw opening forcecounter may increment to the number of loop cycles that the measuredopening force was briefly above the minimum jaw opening force thresholdplus the margin. As long as the measured opening force stays below theminimum jaw opening force threshold plus the margin within a window thatspans a number of loop cycles equaling to the jaw opening force counter(e.g., the number of loop cycles that the measured opening force wasbriefly above the minimum jaw opening force threshold plus the margin),the feedback control loop may still consider the measured opening forceto be smaller than the minimum jaw opening force threshold for theentire duration of the window so as to maintain the minimum jaw openingforce.

When the controller 562 determines that the jaws are opening in theposition mode, the θ_(jaw) error is larger than the θ_(jaw) errorthreshold, and the measured opening force is below the pre-specifiedminimum jaw opening force threshold, the controller may maintain themeasured opening force above the minimum jaw opening force threshold. Inone embodiment, the controller 562 may calculate a jaw opening forceerror that is the difference between the minimum jaw opening forcethreshold and the measured opening force. A zero steady-state typecontroller, such as a proportional plus integral (PI) force controller,may be deployed to receive the jaw opening force error to maintain themeasured opening force at or above the minimum jaw opening forcethreshold. The output of the PI force controller may be combined withthe output of the inverse kinematic matrix that operates on errors inthe desired position and orientation of the wrist jaws to generatecompensated actuator position commands. The compensated actuatorposition commands are added to the existing actuator position commandsto drive the wrist jaws to maintain the minimum amount of opening forcewhen the jaws are opening in the position mode at the desired positionand orientation.

FIG. 8A is a time plot showing the commanded θ_(jaw) 803, the measuredθ_(jaw) 805, the commanded grip force 807, and the measured openingforce 809 of the wrist jaws when the measured opening force 809 is notmaintained above a minimum level while the jaws are opening in theposition mode. The threshold θ_(jaw) between the position mode and theforce mode, is set at zero so that when the commanded θ_(jaw) 603 isgreater than or equal to zero degree, the wrist jaws are operating inthe position mode. When the commanded θ_(jaw) 603 is less than zerodegree, the wrist jaws are operating in the force mode. The θ_(jaw)error threshold is set at 5 degrees and the minimum opening forcethreshold is set at 4.4 N.

FIG. 8A shows that from 49 to 60 second and from 62 to 67 second, thewrist jaws are operating in the position mode. The measured θ_(jaw) 805stays within a relatively narrow range even as the commanded θ_(jaw) 803configures the jaw to close or open within the position mode, presumablybecause the opening jaws in the position mode are meeting resistance orare constrained from opening fully to the commanded θ_(jaw) 803. From49-52 second, 56-59 second, and 62-66 second when the jaws are openingin the position mode or are maintained in the same θ_(jaw), the θ_(jaw)error, the difference between the larger commanded θ_(jaw) 803 and thesmaller measured θ_(jaw) 805, may be larger than the θ_(jaw) errorthreshold of 5 degrees.

During the position mode, the commanded grip force 807 may be set by agrip force controller to a default value of zero N. Even during theforce mode, the commanded grip force 807 is still set to zero N. Apositive value for the measured opening force 809 corresponds to theopening force of the jaws in the position mode and a negative valuecorresponds to the grip force in the force mode when the jaws areclosed. The measured opening force 809 in the position mode generallyfollows the profile of the commanded θ_(jaw) 803 because the jaws areconstrained from opening to the commanded θ_(jaw) 803. The result isstronger measured opening force 809 when the commanded θ_(jaw) 803 isincreased for wider opening of the jaws and conversely weaker measuredopening force 809 when the commanded θ_(jaw) 803 is decreased fornarrower opening of the jaws. Because the feedback control loop is notenabled to maintain the measured opening force 809 above the minimumopening force threshold of 4.4 N, between 53 to 60 second, the measuredopening force 809 may drop below the minimum opening force threshold.

FIG. 8B is a time plot showing the commanded θ_(jaw) 813, the measuredθ_(jaw) 815, the commanded grip force 817, and the measured openingforce 819 of the wrist jaws when a control system maintains the measuredopening force 819 above a pre-specified minimum opening force thresholdduring jaws opening in the position mode, in accordance with aspects ofthe subject technology. The θ_(jaw) error threshold is again set at 5degrees and the minimum opening force threshold is set at 4.4 N.

In FIG. 8B, the time plot of the commanded θ_(jaw) 813 and the measuredθ_(jaw) 815 is generally the same as the commanded θ_(jaw) 803 and themeasured θ_(jaw) 805 of FIG. 8A when the minimum jaw opening force isnot maintained. During the position mode, the commanded grip force 817is again set by the grip force controller to the default value of zeroN. However, the measured opening force 819 is maintained by the feedbackcontrol loop and the grip force controller at or above the minimumopening force threshold of 4.4 N during the position mode between 30-43second when the θ_(jaw) error, the difference between the largercommanded θ_(jaw) 813 and the smaller measured θ_(jaw) 815, is largerthan the θ_(jaw) error threshold of 5 degrees. In particular, when thejaws are opening, maintaining the same θ_(jaw), or even closing in theposition mode, the minimum measured opening force 819 is maintained.Note that minimum opening force threshold in the position mode has noeffect on the force mode when the measured opening force 819 may benegative.

FIG. 9 is a flow chart illustrating a method 900 for feedback control ofa surgical robotic system to maintain the opening force of the wristjaws above a pre-specified minimum jaw opening force threshold duringjaws opening in the position mode by analyzing the desired jaw angle,the estimated jaw angle and the measured opening force, in accordancewith aspects of the subject technology. The method 900 may beimplemented by the controller 562 of the control system of FIG. 5 thatreceives the desired θ_(jaw) from user input, the estimated or themeasured θ_(jaw), and the measured opening force from sensors andestimators 566 to generate actuator position commands for driving thewrist jaws.

In block 901, the method 900 determines if the wrist jaws are in theposition mode. In one embodiment, block 901 may determine if the desiredθ_(jaw) is greater than or equal to the threshold θ_(jaw) between theposition mode and the force mode for more than a pre-specified timeperiod to confirm that the wrist jaws are in the position mode. In oneembodiment, the threshold θ_(jaw) may be set to zero. If the wrist jawsare not in the position mode, the wrist jaws are in the force mode andminimum opening force is not enabled. In block 909, the method 900generates actuator position commands without maintaining a minimumopening force. In one embodiment, block 909 translates the desiredθ_(jaw) into a desired grip force command to achieve the desired gripforce or opening force in addition to generating the actuator positioncommands.

If the jaws are in the position mode, block 903 determine if the jawsare prevented from opening to the desired θ_(jaw) by determining if theθ_(jaw) error, which is the difference between the desired θ_(jaw) andthe estimated or measured θ_(jaw), is larger than or equal to an θ_(jaw)error threshold. In one embodiment, block 903 may employ a debouncingtechnique to determine if the desired θ_(jaw) is larger than theestimated θ_(jaw) and that the θ_(jaw) error is larger than or equal tothe θ_(jaw) error threshold for a pre-specified length of time. In oneembodiment, block 903 may detect that the jaws are opening, maintaininga quiescent θ_(jaw), or closing by determining that the desired θ_(jaw)is increasing, staying the same, or decreasing, respectively. If theθ_(jaw) error is smaller than the θ_(jaw) error threshold, the method900 defaults to block 909 to generate actuator position commands withoutmaintaining a minimum opening force.

If the θ_(jaw) error is larger than or equal to the θ_(jaw) errorthreshold when the jaws are in the position mode, block 905 determinesif the measured opening force is below a pre-specified minimum jawopening force threshold. In one embodiment, block 905 may employ adebouncing technique to determine that the measured opening force isless than the minimum jaw opening force threshold plus a margin anywherewithin a window that spans a number of samples equaling to a jaw openingforce counter. In one embodiment, the measured opening force may besampled at a loop cycle time of the feedback control system of FIG. 5 .The jaw opening force counter may increment by one for every controlloop cycle during which the measured opening force is larger than theminimum jaw opening force threshold plus the margin. When the measuredopening force is less than the minimum jaw opening force threshold, thejaw opening force counter may reset. As long as the measured openingforce is less than the minimum jaw opening force threshold plus themargin anywhere within the window that spans the number of samplesequaling to the jaw opening force counter, the measured opening force isconsidered to be below the minimum jaw opening force threshold for theentire window. Otherwise, the measured opening force is more than orequal to the minimum jaw opening force threshold and the method 900defaults to block 909 to generate actuator position commands withoutmaintaining a minimum opening force.

If the measured opening force is less than the minimum jaw opening forcethreshold and the θ_(jaw) error is larger than or equal to the θ_(jaw)error threshold when the jaws are in the position mode, block 907generates compensated actuator position commands to maintain themeasured opening force above the minimum jaw opening force threshold. Inone embodiment, block 907 may calculate a jaw opening force error thatis the difference between the minimum jaw opening force threshold andthe measured opening force. A zero steady-state type controller, such asa proportional plus integral (PI) force controller, may be deployed toreceive the jaw opening force error to maintain the measured openingforce at or above the minimum jaw opening force threshold. The output ofthe PI force controller may be combined with the output of the inversekinematic matrix that operates on errors in the desired position andorientation of the wrist jaws to generate compensated actuator positioncommands. The compensated actuator position commands are added to theexisting actuator position commands to drive the wrist jaws to maintainthe minimum amount of opening force when the jaws are opening in theposition mode.

In another aspect, the controller 562 may adjust the commanded gripforce to smooth the grip force applied when the wrist jaws transitionbetween the position mode and the force mode. Smoothing the grip forceapplied during mode transitions minimizes undesired sudden changes inthe grip force caused by changes in the position and commanded gripforce of the jaws that may cause the jaws to accidentally drop an objectbeing grasped when the jaws traverse through the point of discontinuitybetween the two modes. During the position mode the desired θ_(jaw) isgreater than or equal to the threshold for detent. A position controllermay translate the desired θ_(jaw), as well as the desired θ_(pitch) anddesired θ_(yaw), into corresponding actuator position commands to drivethe wrist jaws to the desired position and orientation. During the forcemode when the desired θ_(jaw) is below the threshold for detent, forexample when the desired θ_(jaw) is negative for detent set at zerodegree, a grip force controller may be enabled to interpret the desiredθ_(jaw) as a grip force command and may translate the desired θ_(jaw)into compensation current that may be added to current for the existingposition commands to drive the wrist jaws to achieve the commanded gripforce.

In one embodiment, to smooth the grip force applied during modetransitions, a feedback control system may employ a debouncing techniquewhen detent is set at zero degree. The debouncing technique may preventthe grip force controller from repeatedly getting enabled and disabledto create oscillation in the commanded grip force when the desiredθ_(jaw) oscillates around positive and negative values.

In one embodiment, the feedback control system may minimize suddenchanges in the grip force when the wrist jaws transition from theposition mode to the force mode by analyzing the desired θ_(jaw), thecommanded grip force, and the measured grip force. The feedback controlsystem may determine if the commanded grip force is increasing due tothe grip force controller getting enabled as indicated by the desiredθ_(jaw) decreasing below the threshold for detent, and if an errorbetween the measured grip force and the commanded grip force is largerthan a pre-specified maximum force error. If so, the feedback controlsystem may set the commanded grip force as the measured grip force minusa pre-specified margin when the wrist jaws transition from the positionmode to the force mode.

In one embodiment, the feedback control system may minimize suddenchanges in the grip force when the wrist jaws transition from the forcemode to the position mode by analyzing the desired θ_(jaw), thecommanded grip force, and the measured grip force. The feedback controlsystem may determine if the commanded grip force is smaller than apre-specified minimum grip force value, if the commanded grip force isdecreasing due to the grip force controller being disabled as indicatedby the desired θ_(jaw) increasing above the threshold for detent, and ifthe absolute value of an error between the measured grip force and theminimum grip force is smaller than a pre-specified maximum grip forceerror value. If so, the feedback control system may set the commandedgrip force to the pre-specified minimum grip force value when the wristjaws transition from the force mode to the position mode.

FIG. 10 is a block diagram of an exemplary control system 1000 forcontrolling the position and grip force of an end effector of a roboticsurgical tool when the end effector is in the position mode or forcemode, or when the end effector transitions between the position mode andthe force mode, in accordance with aspects of the subject technology. Inone embodiment, the end effector includes wrist jaws. The roboticcontrol system 1000 comprises an input processing unit 502, an actuatorcommand generator 504, a position controller 506, a grip forcecontroller 508, a plant including one or more actuator units 510 and/orcables and wrist links 512, a slack controller 514, a position estimator522 and a grip force estimator 524.

The input processing unit 502 and the actuator command generator 504receive desired angular positions of the wrist jaws and translate thedesired angular positions into corresponding actuator position commands(via inverse kinematics algorithm), which are output to the positioncontroller 506 and/or grip force controller 508. For example, the inputdesired angular positions may include the desired θ_(jaw), desiredθ_(pitch) and desired θ_(yaw). The desired θ_(jaw) may be treated as aposition command when the desired θ_(jaw) is greater than or equal tothe threshold for detent. When the desired θ_(jaw) is less than thethreshold for detent, the desired θ_(jaw) may be translated to a desiredgrip force command (e.g., commanded grip force) by the grip forcecontroller 508, which may generate a current command to achieve thedesired grip force.

The position controller 506 may receive position feedback from positionand/or speed sensors on the actuator units 510. Achieving the desiredactuator positions can in turn lead to the desired position of the wristjaws due to the kinematic relationship between the actuators and thewrist jaws. Since the actuator units 510 are coupled to the roboticwrist through elastic cables (or wires), which may change length underforce, estimation only based on a pure kinematic relation betweenactuator positions and wrist movements may not be accurate. The positionestimator 522 may provide the actuator command generator 504 and thegrip force estimator 524 with a more accurate estimate of the wristjoint positions and velocities by taking into account the cableelasticity in estimation algorithms (e.g., using a Kalman filter). Theestimated position and velocity information can then be used foraccurate positioning of the wrist, as well as estimation of thefriction.

In one embodiment, the grip force controller 508 takes feedback of cabletensions measured by load cells or torque sensors on the cable wires.Algorithms can then be used by the grip force estimator 524 to estimatethe grip force between the jaws based on the tension values measured onthe cables. The grip force controller 508 may compare the estimatedvalue to the desired grip force and generates additional currentcommands to achieve the desired grip force. The wrist jaws may becoupled to the tool drive through four independent cables, each of whichis actuated by an independent motor. In one embodiment, the motors maybe driven by current. The current command may include two parts: thefirst part of the driving current may be from the position controller506 and the second part from the grip force controller 508. The twocurrent commands may be summed up and sent to the actuator units 510.

The slack controller 514 may perform the task of ensuring the tensionson the cables never fall below zero (or a predetermined positive valueto compensate slackness). Cables are tension-only members of the endeffector, to which negative forces cannot be applied. Therefore, it isdesirable to prevent the tensions on the cables from dropping to zero.To achieve this goal, the slack controller 514 may monitor the forcevalues from load cells on the cables and compare the minimum of theforce values to a predetermined threshold. If the minimum force valueacross all the cables falls below the threshold, the slack controller514 may generate an additional position command to all the actuators toensure that the desired minimum tension is maintained.

To smooth the grip force applied during mode transitions, the inputprocessing unit 502 may employ a debouncing technique when detent is setat zero degree. The debouncing technique may determine if the desiredθ_(jaw) is smaller than the threshold for detent for a pre-specifiedminimum duration before enabling the grip force controller 508 totransition the wrist jaws from the position mode to the force mode. Whentransitioning from the force mode to the position mode, the inputprocessing unit 502 may disable the grip controller 508 as soon as thedesired θ_(jaw) is greater than or equal to the threshold for detent.Thus, the debouncing technique may be one-sided. The debouncingtechnique prevents the grip force controller 508 from repeatedly gettingenabled and disabled, a condition that may cause oscillation in thecommanded grip force when the desired θ_(jaw) oscillates around detent.

FIG. 11A is a time plot showing the commanded θ_(jaw) 1103, the measuredθ_(jaw) 1105, the commanded grip force 1107, the measured grip force1109 of the wrist jaws, and the current command 1106 from a grip forcecontroller (e.g., grip force controller 508 of FIG. 10 ) when thecommanded θ_(jaw) 1103 is set to be around the threshold for detentwithout a debouncing algorithm. The threshold for detent is set at zeroso that when the commanded θ_(jaw) 1103 is greater than or equal to zerodegree, the wrist jaws are operating in the position mode. When thecommanded θ_(jaw) 1103 is less than zero degree, the wrist jaws areoperating in the force mode. A positive grip force indicates the gripforce in the force mode and a negative grip force indicates the gripforce in the position mode.

FIG. 11A shows that between time 11.6 and 12 second, the wrist jaws areoperating in the position mode. After time 12 second, the commandedθ_(jaw) 1103 is set around the threshold for detent due to the userinput device (UID) set at detent. The measured θ_(jaw) 1105 stays aboveabout 20 degrees, presumably because the jaws are grasping an object.The grip force controller 508 is repeatedly enabled and disabled whenthe wrist jaws teeters between the position mode and the force mode,causing the oscillations in the commanded grip force 1107 and thecurrent command 1106 from the grip force controller 508 when the gripforce controller 508 is enabled during the force mode. The result is theundesired large swings in the measured grip force 1109 observed betweentime 12 and 12.4 second. The measured θ_(jaw) 1105 also shows someundesired oscillations due to the swings in the measured grip force1109.

FIG. 11B is a time plot showing the commanded θ_(jaw) 1113, the measuredθ_(jaw) 1115, the commanded grip force 1117, the measured grip force1119 of the wrist jaws, and the current command 1116 from the grip forcecontroller 508 when a control system (e.g., input processing unit 502and actuator command generator 504 of FIG. 10 ) employs a debouncingalgorithm when the commanded θ_(jaw) 1113 is set to be around detent, inaccordance with aspects of the subject technology. The threshold fordetent is again set at zero. Between time 30.2 and 30.9 second, thewrist jaws are operating in the position mode. After time 30.9 second,the commanded θ_(jaw) 1113 is set around the threshold for detent.

The debouncing algorithm may enable the grip force controller 508 totransition the wrist jaws from the position mode to the force mode onlyif the desired θ_(jaw) is less than zero degree for a pre-specifiedminimum duration. Because the control system does not detect thiscondition, the wrist jaws remain in the position mode and the grip forcecontroller 508 is not enabled. As a result, the commanded grip force1117 stays at the default value of 0 N and the current command 1116 fromthe grip force controller 508 also stays at 0. The measured grip force1119 exhibits none of the large swings and the measured θ_(jaw) 1115exhibits none of the oscillations observed in FIG. 11A, ensuring asmooth application of the grip force (the measured grip force 1119 isshown as positive even though the wrist jaws remain in the positionmode).

Smooth applications of the grip force may also become important when thewrist jaws are grasping an object when transitioning between theposition mode and the force mode. For example, during the position modeeven though the grip force controller 508 is not enabled, there may benon-zero measured grip force if the wrist jaws are grasping an object.When the desired θ_(jaw) drops below the threshold for detent,indicating a transition from the position mode to the force mode, thegrip force controller 508 may initially drive the commanded grip forcefrom 0 N. Similarly, when transitioning from the force mode to theposition mode, when the grip force controller 508 is disabled, thecommanded grip force may reset to the default value of 0 N output fromthe position controller 506. As a result, there may be a sudden changein the measured grip force during the transitions, potentially causingthe wrist jaws to drop the object.

FIG. 12A is a time plot showing the commanded θ_(jaw) 1203, the measuredθ_(jaw) 1205, the commanded grip force 1207, and the measured grip force1209 of the wrist jaws when a control system does not attempt to limitchanges in the measured grip force 1209 when the wrist jaws transitionfrom the position mode to the force mode and back to the position mode.The threshold for detent is again set at 0 so that when the commandedθ_(jaw) 1203 is greater than or equal to 0 degree, the wrist jaws areoperating in the position mode. When the commanded θ_(jaw) 1203 is lessthan 0 degree, the wrist jaws are operating in the force mode.

The wrist jaws are initially operating in the position mode. Thecommanded θ_(jaw) 1203 is initially at 0 degree and the commanded gripforce 1207 is initially at 0 N. The measured θ_(jaw) 1205 is at 25degrees and the measured grip force 1209 is at 8 N due to an object heldbetween the jaws. At time 27.5 second, the commanded θ_(jaw) 1203becomes negative to transition the wrist jaws from the position mode tothe force mode. When the grip force controller 508 is enabled, thecommanded grip force 1207 ramps up from 0 N until the commanded θ_(jaw)1203 reaches its most negative value. However, the measured grip force1209 experiences a sudden drop of 5 N during the transition beforeramping up as commanded. At time 30 second, the commanded θ_(jaw) 1203starts to become less negative. The commanded grip force 1207 starts toramp down and the measured grip force 1209 follows as commanded. At time31 second, the commanded θ_(jaw) 1203 becomes positive to transition thewrist jaws from the force mode back to the position mode. When the gripforce controller 508 is disabled, the measured grip force 1209experiences a sudden jump from 0 N to the quiescent 8 N of the positionmode with some overshoot. It is desired to minimize sudden changes inthe measured grip force 1209 during the transitions.

In one embodiment, to minimize sudden changes in the grip force of thewrist jaws when holding an object during the transition from theposition mode to the force mode, the grip force controller 508 mayadjust the commanded grip force. For example, the grip force controller508 may set the commanded grip force to be the currently measured gripforce minus a pre-specified margin when the grip force controller 508 isenabled upon the commanded θ_(jaw) becoming less than the threshold fordetent and if certain conditions are satisfied. Doing so may prevent themeasured grip force from dropping to a value close to 0 N during thetransition, thereby reducing the probability of the jaws dropping theobject held between the jaws. In one embodiment, the measured grip forcemay be generated by the grip force estimator 524 based on the tensionvalues measured on the cables from cable and wrist links 512.

To evaluate a first condition for adjusting the commanded grip force,the grip force controller 508 may determine if the commanded grip forceis or will be increasing due to the grip force controller 508 gettingenabled as indicated by the commanded θ_(jaw) decreasing below thethreshold for detent. For a second condition, the grip force controller508 may determine if the error between the measured grip force and thecommanded grip force is larger than a pre-specified maximum force error.In one embodiment, the grip force controller 528 may use a debouncingtechnique for one or both of the conditions. If these two conditions aresatisfied, the grip force controller 508 may set the commanded gripforce to be the currently measured grip force minus the pre-specifiedmargin.

In one embodiment, to minimize sudden changes in the grip force of thewrist jaws when holding an object during the transition from the forcemode to the position mode, the grip force controller 508 may adjust thecommanded grip force. For example, the grip force controller 508 may setthe commanded grip force to a pre-specified minimum grip force valuewhen the grip force controller 508 is disabled upon the commandedθ_(jaw) becoming more than the threshold for detent and if certainconditions are satisfied. Doing so instead of starting from the default0 N of the position mode may reduce the change for the measured gripforce to rise to the quiescent grip force of the position mode.

To evaluate the conditions for adjusting the grip force, the grip forcecontroller 508 may determine if the commanded grip force is smaller thanthe pre-specified minimum grip force value. The grip force controller508 may also determine if the commanded grip force is decreasing asindicated by the commanded θ_(jaw) increasing toward or crossing thethreshold for detent. The grip force controller 508 may additionallydetermine if the absolute value of the error between the measured gripforce and the minimum grip force value is smaller than a pre-specifiedmaximum grip force error value. In one embodiment, the grip forcecontroller 528 may use a debouncing technique for one or more of theconditions. If all the conditions are satisfied, the grip forcecontroller 508 may set the commanded grip force to be the pre-specifiedminimum grip force value. In one embodiment, the pre-specified minimumgrip force value may be set to 3 N.

FIG. 12B is a time plot showing the commanded θ_(jaw) 1213, the measuredθ_(jaw) 1215, the commanded grip force 1217, and the measured grip force1219 of the wrist jaws when a control system limits changes in themeasured grip force 1219 as the wrist jaws transition between theposition mode and the force mode, in accordance with aspects of thesubject technology. The threshold for detent is again set at 0 so thatwhen the commanded θ_(jaw) 1213 is greater than or equal to 0 degree,the wrist jaws are operating in the position mode. When the commandedθ_(jaw) 1213 is less than 0 degree, the wrist jaws are operating in theforce mode. The pre-specified maximum grip force error value, which isnot to be exceeded by the absolute value of the error between themeasured grip force and the commanded grip force, is set to more than 8N. The pre-specified minimum grip force value is set to 3 N.

The wrist jaws are initially operating in the position mode with theinitial states of the commanded θ_(jaw) 1213, measured θ_(jaw) 1215,commanded grip force 1217, and measured grip force 1219 the same as inFIG. 12A. At time 37.4 second, the commanded θ_(jaw) 1203 becomesnegative to transition the wrist jaws from the position mode to theforce mode. However, instead of starting from 0 N in the force mode, thecommanded grip force 1217 starts from about 6.2 N, obtained bysubtracting a pre-specified margin from the measured grip force 1219 atthis time. The conditions for the adjustment to the commanded grip force1217 are satisfied because the absolute value of the error between themeasured grip force 1219 and the commanded grip force 1217 is smallerthan the pre-specified maximum force error. The result is that themeasured grip force 1219 experiences a significantly smaller drop thanwithout the adjustment to the commanded grip force 1217 during thetransition from the position mode to the force mode. The commanded gripforce 1217 stays at 6.2 N until the commanded grip force 1217 asdetermined from the increasingly negative commanded θ_(jaw) 1213 becomesgreater than 6.2 N.

At time 39.8 second, the commanded θ_(jaw) 1213 starts to become lessnegative. The commanded grip force 1217 starts to ramp down and themeasured grip force 1219 follows as commanded. At time 40.5 second, thecommanded grip force 1217 stays at the pre-specified minimum grip forcevalue of 3 N instead of continuing to ramp down to 0 N as otherwisewould have occurred without the adjustment as the commanded θ_(jaw) 1213becomes positive to transition the wrist jaws from the force mode to theposition mode. The conditions for the adjustment to the commanded gripforce 1217 are satisfied because the measured grip force 1219 is smallerthan the pre-specified minimum grip force value of 3 N and the absolutevalue of the error between the measured grip force 1219 and thecommanded grip force 1217 is smaller than the pre-specified maximumforce error. The result is that the measured grip force 1219 experiencesa significantly smaller change than without the adjustment to thecommanded grip force 1217 as the measured grip force 1219 jumps to thequiescent 8 N of the position mode during the transition. The commandedgrip force 1217 stays at 3 N until the commanded grip force 1217 asdetermined from the commanded θ_(jaw) 1213 becomes 0 N.

FIG. 13 is a flow chart illustrating a method 1300 for a feedbackcontrol of a surgical robotic system to employ a debouncing algorithmwhen setting the desired θ_(jaw) of the wrist jaws around the thresholdfor detent, or to adjust the commanded grip force to limit changes inthe measured grip force when the wrist jaws transition between theposition mode and the force mode, in accordance with aspects of thesubject technology. The method 1300 may be implemented by the controller562 of the control system of FIG. 5 or the grip force controller 508 ofthe control system of FIG. 10 that receives the desired θ_(jaw) fromuser input and the measured grip force from sensors and estimators 566of FIG. 5 or the grip force estimator 524 of FIG. 10 , respectively, togenerate commanded grip force for driving the wrist jaws.

Starting from the position mode in block 1301, the method 1300determines if the desired θ_(jaw) is smaller than the threshold fordetent for a minimum duration in block 1303. In one embodiment, theminimum duration may be pre-specified or may be configurable. Block 1303implements a debouncing algorithm to prevent the force mode fromrepeatedly being enabled and disabled, a condition that may causeoscillation in the commanded grip force when the desired θ_(jaw) is setaround the threshold for detent. In one embodiment, block 1303 maydetermine if the commanded grip force is or will be increasing asindicated by the desired θ_(jaw) decreasing below the threshold fordetent. If the desired θ_(jaw) is not smaller than the threshold fordetent for the pre-specified minimum duration, the wrist jaws remain inthe position mode of block 1301.

Otherwise, if the desired θ_(jaw) is smaller than the threshold fordetent for the pre-specified minimum duration, the wrist jaws aretransitioning from the position mode to the force mode. Block 1304determines if the commanded grip force is increasing. If this conditionis false, block 1307 sets the commanded grip force as translated fromthe desired θ_(jaw) and the commanded grip force is not adjusted tolimit changes in the measured grip force during the mode transition.Otherwise, if the condition in block 1304 is true, block 1305 determinesif the error between the measured grip force and the commanded gripforce is larger than a maximum force error during the mode transition.The commanded grip force may be at the default 0 N in the position modeprior to the mode transition. The measured grip force may be differentfrom the commanded grip force prior to the mode transition because thewrist jaws may be grasping an object. In one embodiment, the maximumforce error may be pre-specified or may be configurable.

If the condition in block 1305 is true, block 1309 sets the commandedgrip force to the measured grip force minus a margin when the wrist jawstransition from the position mode to the force mode. In one embodiment,the margin may be pre-specified or may be configurable. Otherwise, ifthe condition in block 1305 is false, block 1307 sets the commanded gripforce as translated from the desired θ_(jaw) and the commanded gripforce is not adjusted to limit changes in the measured grip force duringthe mode transition.

When the wrist jaws are in the force mode in block 1311, the method 1300determines if the desired θ_(jaw) is greater than or equal to thethreshold for detent in block 1313. In one embodiment, block 1311 maydetermine if the commanded grip force is decreasing as indicated by thedesired θ_(jaw) increasing toward the threshold for detent and that thedesired θ_(jaw) is just below the threshold for detent. If the desiredθ_(jaw) is not greater than or equal to the threshold for detent, thewrist jaws remain in the force mode of block 1311.

Otherwise, if the desired θ_(jaw) is greater than or equal to thethreshold for detent, the wrist jaws are transitioning from the forcemode to the position mode. Block 1315 determines if the commanded gripforce is decreasing and if the commanded grip force is less than aminimum grip force during the mode transition. In one embodiment, theminimum grip force may be pre-specified or may be configurable. If thecommanded grip force is not decreasing or if the commanded grip force isnot less than the minimum grip force during the mode transition, block1307 sets the commanded grip force as translated from the desiredθ_(jaw) and the commanded grip force is not adjusted to limit changes inthe measured grip force during the mode transition.

Otherwise, if the commanded grip force is decreasing and if thecommanded grip force is less than the minimum grip force during the modetransition, block 1317 determines if the absolute value of the errorbetween the measured grip force and the minimum grip force value issmaller than a maximum force error during the mode transition. In oneembodiment, the maximum force error may be pre-specified or may beconfigurable. The maximum force error in block 1317 for theforce-to-position mode transition may be the same or different from themaximum force error in block 1305 for the position-to-force modetransition.

If the condition in block 1317 is true, block 1319 sets the commandedgrip force to the minimum grip force when the wrist jaws transition fromthe force mode to the position mode. Otherwise, if the condition inblock 1317 is false, block 1307 sets the commanded grip force astranslated from the desired θ_(jaw) and the commanded grip force is notadjusted to limit changes in the measured grip force during the modetransition.

FIG. 14 is a block diagram illustrating exemplary hardware components ofa surgical robotic system, in accordance with aspects of the subjecttechnology. The surgical robotic system may include an interface device50, a surgical robot 80, and a control tower 70. The surgical roboticsystem may include other or additional hardware components; thus, thediagram is provided by way of example and not a limitation to the systemarchitecture.

The interface device 50 includes a camera 51, sensor 52, display 53,user command interface 54, processor 55, memory 56, and networkinterface 57. The camera 51 and the sensor 52 may be configured tocapture color images and depth-image information of the surgical roboticsystem. Images captured by the camera 51 and sensor 52 may be projectedon the display 53. The processor 55 may be configured to run anoperating system to control the operation of the interface device 50.The memory 56 may store the image processing algorithms, operatingsystem, program codes, and other data memories used by the processor 55.The interface device 50 may be used to generate the desired θ_(pitch),θ_(yaw), and θ_(jaw) of the wrist jaws under the control of a remoteoperator.

The user command interface 54 may include the interface for otherfeatures such as the Web portal. The hardware components may communicatevia a bus. The interface device may use the network interface 57 tocommunicate with the surgical robotic system through an externalinterface. The external interface may be a wireless or a wiredinterface.

The control tower 70 may be a mobile point-of-care cart housingtouchscreen displays, computers that control the surgeon'srobotically-assisted manipulation of instruments, safety systems,graphical user interface (GUI), light source, and video and graphicscomputers. The control tower 70 may comprise central computers 71 thatmay include at least a visualization computer, a control computer, andan auxiliary computer, various displays 73 that may include a teamdisplay and a nurse display, and a network interface 78 coupling thecontrol tower 70 to both the interface device 50 and the surgical robot80. The control tower 70 may also house third-party devices, such as anadvanced light engine 72, an electrosurgical generator unit (ESU) 74,and insufflator and CO₂ tanks 75. The control tower 70 may offeradditional features for user convenience, such as the nurse displaytouchscreen, soft power and E-hold buttons, user-facing USB for videoand still images, and electronic caster control interface. The auxiliarycomputer may also run a real-time Linux, providing logging/monitoringand interacting with cloud-based web services. The central computers 71of the control tower 70 may receive the desired θ_(pitch), θ_(yaw), andθ_(jaw) of the wrist jaws generated by the interface device 50 toimplement the methods described herein for controlling the grip force oropening force of the jaws.

The surgical robot 80 comprises an articulated operating table 84 with aplurality of integrated arms 82 that may be positioned over the targetpatient anatomy. A suite of compatible tools 83 may be attached to ordetached from the distal ends of the arms 82, enabling the surgeon toperform various surgical procedures. The surgical robot 80 may alsocomprise control interface 85 for manual control of the arms 82,operating table 84, and tools 83. The control interface 85 may includeitems such as, but not limited to, remote controls, buttons, panels, andtouchscreens. Other accessories such as trocars (sleeves, sealcartridge, and obturators) and drapes may also be manipulated to performprocedures with the system. In one embodiment, the plurality of the arms82 may include four arms mounted on both sides of the operating table84, with two arms on each side. For certain surgical procedures, an armmounted on one side of the operating table 84 may be positioned on theother side of the operating table 84 by stretching out and crossing overunder the operating table 84 and arms mounted on the other side,resulting in a total of three arms positioned on the same side of theoperating table 84. The surgical tool may also comprise table computers81 and a network interface 88, which may place the surgical robot 80 incommunication with the control tower 70.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the invention.However, it will be apparent to one skilled in the art that specificdetails are not required in order to practice the invention. Thus, theforegoing descriptions of specific embodiments of the invention arepresented for purposes of illustration and description. They are notintended to be exhaustive or to limit the invention to the precise formsdisclosed; obviously, many modifications and variations are possible inview of the above teachings. The embodiments were chosen and describedin order to best explain the principles of the invention and itspractical applications. They thereby enable others skilled in the art tobest utilize the invention and various embodiments with variousmodifications as are suited to the particular use contemplated. It isintended that the following claims and their equivalents define thescope of the invention.

The methods, devices, processing, and logic described above may beimplemented in many different ways and in many different combinations ofhardware and software. The controllers and estimators may compriseelectronic circuitry. For example, all or parts of the implementationsmay be circuitry that includes an instruction processor, such as aCentral Processing Unit (CPU), microcontroller, or a microprocessor; anApplication Specific Integrated Circuit (ASIC), Programmable LogicDevice (PLD), or Field Programmable Gate Array (FPGA); or circuitry thatincludes discrete logic or other circuit components, including analogcircuit components, digital circuit components or both; or anycombination thereof. The circuitry may include discrete interconnectedhardware components and/or may be combined on a single integratedcircuit die, distributed among multiple integrated circuit dies, orimplemented in a Multiple Chip Module (MCM) of multiple integratedcircuit dies in a common package, as examples.

The circuitry may further include or access instructions for executionby the circuitry. The instructions may be stored in a tangible storagemedium that is other than a transitory signal, such as a flash memory, aRandom Access Memory (RAM), a Read Only Memory (ROM), an ErasableProgrammable Read Only Memory (EPROM); or on a magnetic or optical disc,such as a Compact Disc Read Only Memory (CDROM), Hard Disk Drive (HDD),or other magnetic or optical disk; or in or on another machine-readablemedium. A product, such as a computer program product, may include astorage medium and instructions stored in or on the medium, and theinstructions when executed by the circuitry in a device may cause thedevice to implement any of the processing described above or illustratedin the drawings.

The implementations may be distributed as circuitry among multiplesystem components, such as among multiple processors and memories,optionally including multiple distributed processing systems.Parameters, databases, and other data structures may be separatelystored and managed, may be incorporated into a single memory ordatabase, may be logically and physically organized in many differentways, and may be implemented in many different ways, including as datastructures such as linked lists, hash tables, arrays, records, objects,or implicit storage mechanisms. Programs may be parts (e.g.,subroutines) of a single program, separate programs, distributed acrossseveral memories and processors, or implemented in many different ways,such as in a library, such as a shared library (e.g., a Dynamic LinkLibrary (DLL)). The DLL, for example, may store instructions thatperform any of the processing described above or illustrated in thedrawings, when executed by the circuitry.

Also, the various controllers discussed herein can take the form ofprocessing circuitry, a microprocessor or processor, and acomputer-readable medium that stores computer-readable program code(e.g., firmware) executable by the (micro)processor, logic gates,switches, an application specific integrated circuit (ASIC), aprogrammable logic controller, and an embedded microcontroller, forexample. The controller can be configured with hardware and/or firmwareto perform the various functions described below and shown in the flowdiagrams. Also, some of the components shown as being internal to thecontroller can also be stored external to the controller, and othercomponents can be used.

What is claimed is:
 1. A method for controlling grip force generated byjaws of a gripper tool of a surgical robotic system, comprising:receiving, by a processor, an input jaw angle; determining, by theprocessor, based on changes of the input jaw angle relative to athreshold jaw angle that the jaws are transitioning between a positionmode and a force mode, the position mode being characterized bypositioning an angle of the jaws at the input jaw angle, and the forcemode being characterized by driving a grip force of the jaws to acommanded grip force, wherein the commanded grip force is determinedbased on the input jaw angle being below the threshold jaw angle;measuring the grip force between the jaws to generate a measured gripforce; determining, by the processor, based on the commanded grip forceand the measured grip force whether to adjust the commanded grip forceduring the transitioning between the position mode and the force mode;and adjusting, by the processor, the commanded grip force during thetransitioning between the position mode and the force mode in responseto determining to adjust the commanded grip force.
 2. The method ofclaim 1, wherein determining that the jaws are transitioning between theposition mode and the force mode comprises: determining that the jawsare transitioning from the position mode to the force mode when theinput jaw angle is initially larger than or equal to zero and becomessmaller than zero for a minimum time duration; or determining that thejaws are transitioning from the force mode to the position mode when theinput jaw angle is initially smaller than zero and becomes larger thanor equal to zero.
 3. The method of claim 1, wherein determining that thejaws are transitioning between the position mode and the force modecomprises: determining, by the processor, that the jaws are initially inthe position mode when the input jaw angle is greater than or equal tothe threshold jaw angle, wherein the threshold jaw angle is when thejaws simultaneously contact an object when the object is being heldbetween the jaws or when the jaws begin to touch each other when thereis no object being held; and determining, by the processor, that thejaws transition from the position mode to the force mode when the inputjaw angle becomes less than the threshold jaw angle for more than aminimum time duration.
 4. The method of claim 3, wherein determiningwhether to adjust the commanded grip force during the transitioningcomprises: determining, by the processor, to adjust the commanded gripforce when the commanded grip force is increasing and a differencebetween the measured grip force and the commanded grip force is largerthan a maximum grip force error during the transitioning from theposition mode to the force mode.
 5. The method of claim 4, whereinadjusting the commanded grip force comprises: setting, by the processor,the commanded grip force to the measured grip force minus a margin inresponse to determining to adjust the commanded grip force; or setting,by the processor, the commanded grip force based on the input jaw anglein the force mode.
 6. The method of claim 1, wherein determining thatthe jaws are transitioning between the position mode and the force modecomprises: determining, by the processor, that the jaws are initially inthe force mode when the input jaw angle is smaller than the thresholdjaw angle, wherein the threshold jaw angle is when the jawssimultaneously contact an object when the object is being held betweenthe jaws or when the jaws begin to touch each other when there is noobject being held; and determining, by the processor, that jawstransition from the force mode to the position mode when the input jawangle becomes larger than or equal to the threshold jaw angle.
 7. Themethod of claim 6, wherein determining whether to adjust the commandedgrip force during the transitioning comprises: determining, by theprocessor, to adjust the commanded grip force when the commanded gripforce is decreasing, the commanded grip force is less than a minimumgrip force, and an absolute value of a difference between the measuredgrip force and the minimum grip force is less than a maximum grip forceerror during the transitioning from the force mode to the position mode.8. The method of claim 7, wherein adjusting the commanded grip forcecomprises: setting, by the processor, the commanded grip force to theminimum grip force in response to determining to adjust the commandedgrip force; or setting, by the processor, the commanded grip force basedon the input jaw angle otherwise.
 9. The method of claim 1, furthercomprising: changing, by the processor, the commanded grip force to bebased on the input jaw angle in the force mode following thetransitioning from the position mode to the force mode when thecommanded grip force is adjusted; or changing, by the processor, thecommanded grip force to be based on the input jaw angle in the positionmode following the transitioning from the force mode to the positionmode when the commanded grip force is adjusted.
 10. An apparatus tocontrol jaws of a gripper tool of a surgical robotic system, comprising:a sensor configured to estimate a grip force between the jaws togenerate a measured grip force; a processor configured to: receive adesired jaw angle; determine that a control mode for operating the jawsis to transition between a position mode and a force mode based onchanges of the desired jaw angle with respect to a threshold jaw angle,the position mode being characterized by positioning an angle betweenthe jaws at the desired jaw angle, and the force mode beingcharacterized by driving a grip force of the jaws to a commanded gripforce, wherein the commanded grip force is determined based on thedesired jaw angle being below the threshold jaw angle; determine whetherto adjust the commanded grip force during the transition between theposition mode and the force mode based on the commanded grip force andthe measured grip force; and adjust the commanded grip force during thetransition between the position mode and the force mode in response tothe determination to adjust the commanded grip force.
 11. The apparatusof claim 10, wherein the processor configured to determine that the jawstransition between the position mode and the force mode comprises:determine that the jaws transition from the position mode to the forcemode when the desired jaw angle is initially larger than or equal tozero and becomes smaller than zero for a minimum time duration; ordetermine that the jaws transition from the force mode to the positionmode when the desired jaw angle is initially smaller than zero andbecomes larger than or equal to zero.
 12. The apparatus of claim 10,wherein the processor configured to determine that the jaws transitionbetween the position mode and the force mode comprises: determine thatthe jaws are initially in the position mode when the desired jaw angleis greater than or equal to the threshold jaw angle, wherein thethreshold jaw angle is when the jaws simultaneously contact an objectwhen the object is being held between the jaws or when the jaws begin totouch each other when there is no object being held; and determine thatthe jaws transition from the position mode to the force mode when thedesired jaw angle becomes less than the threshold jaw angle for morethan a minimum time duration.
 13. The apparatus of claim 12, wherein theprocessor configured to determine whether to adjust the commanded gripforce during the transition comprises: determine to adjust the commandedgrip force when the commanded grip force is increasing and a differencebetween the measured grip force and the commanded grip force is largerthan a maximum grip force error during the transition from the positionmode to the force mode.
 14. The apparatus of claim 13, wherein theprocessor configured to adjust the commanded grip force comprises: setthe commanded grip force to the measured grip force minus a margin inresponse to the determination to adjust the commanded grip force; or setthe commanded grip force based on the desired jaw angle in the forcemode otherwise.
 15. The apparatus of claim 10, wherein the processorconfigured to determine that the jaws transition between the positionmode and the force mode comprises: determine that the jaws are initiallyin the force mode when the desired jaw angle is smaller than thethreshold jaw angle, wherein the threshold jaw angle is when the jawssimultaneously contact an object when the object is being held betweenthe jaws or when the jaws begin to touch each other when there is noobject being held; and determine that the jaws transition from the forcemode to the position mode when the desired jaw angle becomes larger thanor equal to the threshold jaw angle.
 16. The apparatus of claim 15,wherein the processor configured to determine whether to adjust thecommanded grip force during the transition comprises: determine toadjust the commanded grip force when the commanded grip force isdecreasing, the commanded grip force is less than a minimum grip force,and an absolute value of a difference between the measured grip forceand the minimum grip force is less than a maximum grip force errorduring the transition from the force mode to the position mode.
 17. Theapparatus of claim 16, wherein the processor configured to adjust thecommanded grip force comprises: set the commanded grip force to theminimum grip force in response to the determination to adjust thecommanded grip force; or set the commanded grip force based on thedesired jaw angle in the force mode otherwise.
 18. The apparatus ofclaim 10, where the processor is further configured to: change thecommanded grip force to be based on the desired jaw angle in the forcemode subsequent to the transition from the position mode to the forcemode when the processor is configured to adjust the commanded gripforce; or change the commanded grip force to be based on the desired jawangle in the position mode subsequent to the transition from the forcemode to the position mode when the processor is configured to adjust thecommanded grip force.
 19. A surgical robotic system, comprising: an endeffector including a pair of jaws; a user interface device configured togenerate an input jaw angle for the jaws; a processor communicativelycoupled to the end effector, the processor configured to: determine thatthe jaws transition between a position mode and a force mode based onchanges of the input jaw angle with respect to a threshold jaw angle,the position mode being characterized by positioning an angle betweenthe jaws at the input jaw angle, and the force mode being characterizedby driving a grip force of the jaws to a commanded grip force whereinthe commanded grip force is determined based on the input jaw anglebeing below the threshold jaw angle; measure a grip force between thepair of jaws to generate a measured grip force; determine whether toadjust the commanded grip force during the transition between theposition mode and the force mode based on the commanded grip force andthe measured grip force; and adjust the commanded grip force during thetransition between the position mode and the force mode in response tothe determination to adjust the commanded grip force.
 20. The surgicalrobotic system of claim 19, wherein the processor configured todetermine that the jaws transition between the position mode and theforce mode comprises: determine that the jaws are initially in theposition mode when the input jaw angle is greater than or equal to thethreshold jaw angle, wherein the threshold jaw angle is when the jawssimultaneously contact an object when the object is being held betweenthe jaws or when the jaws begin to touch each other when there is noobject being held; and determine that that the jaws transition from theposition mode to the force mode when the input jaw angle becomes lessthan the threshold jaw angle for more than a minimum time duration, andwherein the processor configured to determine whether to adjust thecommanded grip force during the transition comprises: determine toadjust the commanded grip force when the commanded grip force isincreasing and a difference between the measured grip force and thecommanded grip force is larger than a maximum grip force error duringthe transition from the position mode to the force mode, and wherein theprocessor configured to adjust the commanded grip force comprises: setthe commanded grip force to the measured grip force minus a margin inresponse to the determination to adjust the commanded grip force; or setthe commanded grip force based on the input jaw angle in the force modeotherwise.